Nondestructive Detection of the Gel State of Preserved Eggs Based on Dielectric Impedance

Abstract

After completing the production of preserved eggs, traditionally, the degree of gelling is judged by allowing workers to tap the preserved eggs with their fingers and sense the resulting oscillations. The amount of oscillation is used for the quality classification. This traditional method produces varying results owing to the differences in the sensitivity of the individual workers, who are not objective. In this study, dielectric detection technology was used to classify the preserved eggs nondestructively. The impedance in the frequency range of 2–300 kHz was resolved into resistance and reactance, and was plotted on a Nyquist diagram. Next, the diagram curve was fitted in order to obtain the equivalent circuit, and the difference in the compositions of the equivalent circuits corresponding to gelled and non-gelled preserved eggs was analyzed. A preserved egg can be considered an RLC series circuit, and its decay rate is consistent with the decay rate given by mechanical vibration theory. The Nyquist diagrams for the resistance and reactance of preserved eggs clearly showed that the resistance and reactance of gelled and non-gelled eggs were quite different, and the classification of the eggs was performed using Bayesian network (BN). The results showed that a BN classifier with two variables, i.e., resistance and reactance, can be used to classify preserved eggs as gelled or non-gelled, with an accuracy of 81.0% and a kappa value of 0.62. Thus, a BN classifier based on resistance and reactance demonstrates the ability to classify the quality of preserved egg gel. This research provides a nondestructive method for the inspection of the quality of preserved egg gel, and provides a theoretical basis for the development of an automated preserved egg inspection system that can be used as the scientific basis for the determination of the quality of preserved eggs.

Real-Time Gauging of the Gelling Maturity of Duck Eggs Pickled in Strong Alkaline Solutions

“…Traditionally, the manual inspection of pickled eggs is performed by tapping a finger on the eggshells. A pickled egg with good gelation usually oscillates after finger tapping, but those that are liquid or incompletely gelled will not oscillate [ 5 , 18 ]. All the 70 duck eggs used in the experiment passed the tapping examination, indicating that they were all successfully pickled.…”

“…The normalized transmittance (nT( λ 1 )) of Brand B is mainly distributed at −0.4. It is unclear why the shape of the pointed end of the pickled eggs differs between the two factories, but the difference in pickling time (30–40 days) [ 5 ] may be responsible for the discrepancy. Therefore, future studies should focus on minimizing the hydration and dissolution of the pointed end of pickled duck eggs by determining the best pickling time for duck eggs.…”

“…Such strong alkalis slowly permeate through the eggshells and eggshell membranes of the eggs, causing the proteins of the egg whites to undergo a series of chemical changes and gradually changing the albumen’s gel-like structure [ 4 ]. The immersion method entails marinating pickled eggs with salt, tea, and other substances that are usually mixed with sodium hydroxide or potassium hydroxide in specific ratios [ 5 ]. To adjust the osmotic pressure of the alkaline solution used in pickling eggs and increase the success rate of the preserving process, minute amounts of metal salt compounds are added to the pickling solution [ 4 , 5 , 6 ].…”

“…The immersion method entails marinating pickled eggs with salt, tea, and other substances that are usually mixed with sodium hydroxide or potassium hydroxide in specific ratios [ 5 ]. To adjust the osmotic pressure of the alkaline solution used in pickling eggs and increase the success rate of the preserving process, minute amounts of metal salt compounds are added to the pickling solution [ 4 , 5 , 6 ]. Using this method, the time required to produce pickled eggs depends on the concentration of the alkaline solution, the type and concentration of the used metal compounds, and the temperature of the pickling environment.…”

Duck Eggshell Crack Detection by Nondestructive Sonic Measurement and Analysis

“…For human consumption, eggs from chickens and ducks are commonly used. According to statistics from the Duck Breeding Association of the Republic of China, Taiwan's annual production of duck eggs is approximately 460 million, with a total annual output value of approximately 56 million US dollars [5]. Traditionally, duck eggs can be boiled and eaten directly; they can also be used as raw materials for processing.…”